Every piece of information in a table needs to be as simple as possible. So, no tables inside tables, and each column should hold only one kind of data.
Make sure all the information in your table is directly related to the main point of the table, which is usually the primary key. If you have a table with a bunch of stuff in it, make sure each thing is only related to the whole table, not just part of it.
Make sure that all the information in your table is only talking about the primary key, not other non-primary key columns. And make sure none of the non-primary key columns are related to each other. Everything should be connected directly to the main point of the table, which is usually the primary key.